<PAGE>

                                                                   EXHIBIT 10.49


                     FIFTH AMENDMENT TO SUBLEASE AGREEMENT

         THIS FIFTH AMENDMENT (the "Amendment") is made and entered into as of
the 10th day of July, 2000, by and between EOP-PERIMETER CENTER, L.L.C., a
Delaware limited liability company ("Sublessor"), and INTERLIANT, INC., a
Delaware corporation ("Sublessee").

                                   RECITALS

A.   Sublessor (as successor in interest to Southern Company Services, Inc.) and
     Sublessee (formerly known as Sage Networks, Inc.) are parties to that
     certain sublease agreement dated May 29, 1998 (the "Original Sublease") for
     certain space in the building known as 64 Perimeter Center East (formerly
     known as Building 64A) located at 64 Perimeter Center East, Atlanta,
     Georgia (the "Building"). The Original Sublease has been amended by that
     certain First Amendment to Sublease Agreement dated December 9, 1998 (the
     "First Amendment"), that certain Second Amendment to Sublease Agreement
     dated October 31, 1999 (the "Second Amendment"), that certain Third
     Amendment to Sublease Agreement dated February 10, 2000 (the "Third
     Amendment"), and that certain Amendment to Sublease dated June 23, 2000
     (the "Fourth Amendment") (the Original Sublease, as amended as aforesaid,
     is referred as the "Sublease").

B.   The premises currently demised under the Sublease are located in the
     Building and consist of approximately 22,819 rentable square feet of data
     center space (referred to herein as the "Sublease Premises"), comprised of
     the following: (i) approximately 7,240 rentable square feet on floor G1 of
     the Building described as Suite G-300 (the "Original Data Center
     Premises"), (ii) approximately 10,218 rentable square feet on Floor G2 of
     the Building described as the "Data Center Expansion Premises" (as defined
     in the First Amendment), and (iii) approximately 5,361 rentable square feet
     on Floor G2 of the Building described as the "Second Amendment Data Center
     Premises" (as defined in the Second Amendment). The premises demised under
     the Sublease, as described in this Recital B, collectively are referred to
     as the "Original Sublease Premises" or, as appropriate, as the "Original
     Data Center Space".

C.   The premises demised under the Sublease also previously included
     approximately 13,468 rentable square feet on the first floor of the
     Building described as the "Temporary Office Space" (as defined in the First
     Amendment), but the term for the Temporary Office Space expired on May 15,
     2000. Therefore, the Temporary Office Space is no longer included as part
     of the premises demised under the Sublease.

D.   Sublessee has requested that additional space containing approximately
     2,782 rentable square feet described as Suite No. G-255 on Floor G2 of the
     Building shown on Exhibit A hereto (the "Expansion Space") be added to the
     premises demised under the Sublease. Sublessor is willing to add the
     Expansion Space to the Sublease Premises upon the terms and conditions
     hereinafter set forth.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
herein contained and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Sublessor and Sublessee agree as
follows:

I.   Expansion and Effective Date.

     A.   Effective as of August 1, 2000 (the "Expansion Effective Date"), the
          Sublease Premises, as defined in the Sublease, is increased from
          22,819 rentable square feet to 25,601 rentable square feet by the
          addition of the Expansion Space, and from and after the Expansion
          Effective Date, the Original Sublease Premises (as defined in Recital
          B above) and the Expansion Space, collectively, shall be deemed the
          Sublease Premises, as defined in the Sublease. The Term for the
          Expansion Space shall commence on the Expansion Effective Date and end
          on the expiration of the Term, which, unless sooner terminated in
          accordance with the Sublease, shall mean February 28, 2006. (Such
          date, for purposes of this Amendment and the Sublease, is referred to
          as the "Termination Date").

     B.   The Expansion Space is subject to all the terms and conditions of the
          Sublease except as expressly modified herein and except that Sublessee
          shall not be

                                       1
<PAGE>

          entitled to receive any allowances, abatements or other financial
          concessions granted with respect to the Original Sublease Premises
          unless such concessions are expressly provided for herein with respect
          to the Expansion Space. The parties agree that the Expansion Space is
          also subject to all provisions of the Sublease which are specifically
          applicable to Sublessee's data center space within the Sublease
          Premises, including, without limitation, Section 8 of the Original
          Sublease and Section 4(c) of the Second Amendment.

II.  Monthly Base Rent.

     In addition to Sublessee's obligation to pay Base Rent for the Original
     Sublease Premises, Sublessee shall pay Sublessor Base Rent for the
     Expansion Space in 67 monthly installments as follows:

     A.   Twelve (12) equal installments of $6,108.81 (i.e. $26.35 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2000
          and ending July 31, 2001.

     B.   Twelve (12) equal installments of $6,291.96 (i.e. $27.14 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2001
          and ending July 31, 2002.

     C.   Twelve (12) equal installments of $6,479.74 (i.e. $27.95 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2002
          and ending July 31, 2003.

     D.   Twelve (12) equal installments of $6,674.48 (i.e. $28.79 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2003
          and ending July 31, 2004.

     E.   Twelve (12) equal installments of $6,873.86 (i.e. $29.65 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2004
          and ending July 31, 2005.

     F.   Seven (7) equal installments of $7,080.19 (i.e. $30.54 per annum per
          rentable square foot in the Expansion Space) each payable on or before
          the first day of each month during the period beginning August 1, 2005
          and ending February 28, 2006.

     All such Base Rent shall be payable by Sublessee in accordance with the
     terms of the Sublease.

III. Letter of Credit.

     A.   Section 7 of the Original Sublease (Letter of Credit) is amended by
          changing all references to the amount required under the letter of
          credit described therein from $99,999.00 to $191,581.75 (the "Revised
          LOC Amount"). Section 7(b) and Section 7(c) of the Original Sublease
          are deleted in their entirety, it being agreed that the intended
          reductions in the amount required under the letter of credit, as
          described in such subsections, are reflected in the Revised LOC Amount
          described above. In accordance with the foregoing, Section 9 of the
          First Amendment and Section 7 of the Second Amendment are also deemed
          deleted and are of no further force or effect. The Replacement Letter
          of Credit (as defined below) shall provide that, so long Sublessee is
          not late on the payment of any sums payable by Sublessee under the
          Sublease during the 12 month period immediately preceding the
          effective date of any scheduled reduction in the Revised LOC Amount,
          the Revised LOC Amount shall automatically reduce by $8,000.00
          effective as of each of July 1, 2001, July 1, 2002, and July 1, 2003.

     B.   Prior to Sublessee commencing any demolition or construction work in
          the Expansion Space, Sublessee shall deliver to Sublessor a
          replacement letter of credit (the "Replacement Letter of Credit"), in
          the form attached hereto as Exhibit C, for the Revised LOC Amount.
          Upon receipt of the Replacement Letter of Credit in the Revised LOC
          Amount, Sublessor shall return to Sublessee the

                                       2
<PAGE>

          original letter of credit that Sublessor has in its possession which
          was originally delivered pursuant to the terms of Section 7 of the
          Sublease.

IV.  Sublessee's Share of Other Charges. For the period commencing with the
     Expansion Effective Date and ending on the Termination Date, Sublessee
     shall pay for its Share of Other Charges applicable to the Expansion Space
     in accordance with the terms of Section 28 of the Sublease, as amended.
     However, it is specifically agreed that Base Rent for the Expansion Space
     includes, and there shall be no separate charge to Sublessee for,
     Sublessor's costs and expenses for the maintenance set forth on Exhibit "C"
                                                                     ----------
     attached to the Second Amendment.

V.   Improvements to Expansion Space.

     A.   Condition of Expansion Space. Sublessee has inspected the Expansion
          Space and agrees to accept the same "as is" without any agreements,
          representations, understandings or obligations on the part of
          Sublessor to perform any alterations, repairs or improvements.

     B.   Responsibility for Improvements to Expansion Space. Sublessee shall
          perform improvements to the Expansion Space pursuant to the Work
          Letter attached hereto as Exhibit B.

VI.  Early Access to Expansion Space. During any period that Sublessee shall be
     permitted to enter the Expansion Space prior to the Expansion Effective
     Date for reasons other than to commence business operations therein (e.g.,
     to perform alterations or improvements, if any), Sublessee shall comply
     with all terms and provisions of the Sublease, except those provisions
     requiring payment of Base Rent as to the Expansion Space. If Sublessee
     takes possession of the Expansion Space prior to the Expansion Effective
     Date for purposes of commencing business operations therein, such
     possession shall be subject to all the terms and conditions of the Sublease
     and this Amendment, and Sublessee shall pay Base Rent and Sublessee's Share
     of Other Charges as applicable to the Expansion Space to Sublessor on a per
     diem basis for each day of occupancy prior to the Expansion Effective Date.

VII. Other Pertinent Provisions. Sublessor and Sublessee agree that, effective
     as of the date of this Amendment (unless different effective date(s) is/are
     specifically referenced in this Section), the Sublease shall be amended in
     the following additional respects:

     A.   Address for Rent Payments. Section 1(c) of the Sublease, as amended,
          -------------------------
          is hereby amended to reflect that payments of Rent shall be addressed
          as follows:

          Payments of Rent shall be made payable to the order of Equity Office
          Properties and forwarded to the following address:

          EOP Operating Limited Partnership, as agent
          for EOP-Perimeter Center, L.L.C. - Group II
          P.O. Box 931648
          Atlanta, Georgia  31193-1648

     B.   Sublessor Notice Addresses.  Section 53 of the Sublease,  as amended,
          --------------------------
          is hereby amended to reflect that notices to Sublessor shall be
          addressed as follows:

          EOP-Perimeter Center, L.L.C.
          c/o Equity Office Properties Trust
          70 Perimeter Center East, Suite 7016
          Atlanta, Georgia  30346
          Attention:  Building Manager - Group II

          With a copy to:

          Equity Office Properties Trust
          Two North Riverside Plaza
          Suite 2200
          Chicago, Illinois 60606
          Attention:  Regional Counsel - Southeast Region

                                       3
<PAGE>

          B.   Sublessee Notice Addresses.  Section 53 of the Sublease,  as
               --------------------------
               amended, is hereby amended to reflect that notices to Sublessee
               shall be addressed as follows:

               Interliant, Inc.
               66 Perimeter Center East, Suite 800
               Atlanta, Georgia  30346

               With a copy to:

               Interliant, Inc.
               2 Manhattanville Road
               Purchase, New York 10577
               Attention:  General Counsel

          C.   Parking. Effective as of the Expansion Effective Date, in
               -------
               accordance with Section 8 of the First Amendment (Parking
               Arrangements), which replaced Section 35 of the Original
               Sublease, Sublessee shall be entitled to 4 additional parking
               passes with respect to the Expansion Space for parking by
               Sublessee's invitees and employees, free of charge, during the
               remainder of the Term on a first come, first serve basis. Such
               additional passes are in satisfaction of, and not in addition to,
               the 2 parking passes per 1,000 rentable square feet of data
               center space which Sublessee would be entitled to under said
               Section 8 of the First Amendment with respect to the Expansion
               Space. The use of such parking passes shall be subject to the
               terms of Section 8 of the First Amendment, as amended. Further,
               the parties agree that Sublessor shall have the right from time
               to time to promulgate reasonable rules and regulations regarding
               the parking garage, surface parking areas, the spaces and the use
               thereof, including, but not limited to, rules and regulations
               controlling the flow of traffic to and from various parking
               areas, the angle and direction of parking and the like. Sublessee
               shall comply with and cause its employees to comply with all such
               rules and regulations as well as all reasonable additions and
               amendments thereto.

          D.   Deleted  Provision. Section 5 of the Sublease (Renewal Right)
               ------------------
               has been exercised and is therefore of no further force or
               effect.

VIII.     Miscellaneous.

          A.   This Amendment sets forth the entire agreement between the
               parties with respect to the matters set forth herein. There have
               been no additional oral or written representations or agreements.

          B.   Except as herein modified or amended, the provisions, conditions
               and terms of the Sublease shall remain unchanged and in full
               force and effect.

          C.   In the case of any inconsistency between the provisions of the
               Sublease and this Amendment, the provisions of this Amendment
               shall govern and control.

          D.   Submission of this Amendment by Sublessor is not an offer to
               enter into this Amendment but rather is a solicitation for such
               an offer by Sublessee. Sublessor shall not be bound by this
               Amendment until Sublessor has executed and delivered the same to
               Sublessee.

          E.   The capitalized terms used in this Amendment shall have the same
               definitions as set forth in the Sublease to the extent that such
               capitalized terms are defined therein and not redefined in this
               Amendment.

          F.   Sublessee hereby represents to Sublessor that Sublessee has dealt
               with no broker other than The Wesley Company in connection with
               this Amendment. Sublessee agrees to indemnify and hold Sublessor,
               its members, principals, beneficiaries, partners, officers,
               directors, employees, mortgagee(s) and agents, and the respective
               principals and members of any such agents (collectively, the
               "Sublessor Related Parties") harmless from all claims of any
               brokers claiming to have represented Sublessee other than The
               Wesley Company in connection with this

                                       4
<PAGE>

               Amendment. Sublessor hereby represents to Sublessee that
               Sublessor has dealt with no broker other than The Wesley Company
               in connection with this Amendment. Sublessor agrees to indemnify
               and hold Sublessee, its members, principals, beneficiaries,
               partners, officers, directors, employees, and agents, and the
               respective principals and members of any such agents
               (collectively, the "Sublessee Related Parties") harmless from all
               claims of any brokers claiming to have represented Sublessor
               other than The Wesley Company in connection with this Amendment.

         IN WITNESS WHEREOF, Sublessor and Sublessee have duly executed this
Amendment as of the day and year first above written.


                                  SUBLESSOR:

                                  EOP-PERIMETER CENTER, L.L.C., a Delaware
                                  limited liability company

                                  By:  EOP  Operating  Limited   Partnership,
                                       a Delaware limited partnership, its sole
                                       member

                                       By: Equity Office Properties Trust, a
                                           Maryland real estate investment
                                           trust, its managing general partner

                                           By:  /s/ Jeff Sweeney
                                              ----------------------------------
                                           Name:    Jeff Sweeney
                                                --------------------------------
                                           Title:   V.P. Leasing
                                                 -------------------------------


                                  SUBLESSEE:

                                  INTERLIANT, INC., a Delaware corporation

                                  By:  /s/ Kristian Nelson
                                      -----------------------------------------
                                  Name: Kristian Nelson
                                       ----------------------------------------
                                  Title:  SVP of Operations
                                        ---------------------------------------

                                       5
<PAGE>

                                    EXHIBIT A

                                Expansion Space

                                 [FLOOR PLAN]

                                       6
<PAGE>

                                    EXHIBIT B
                                    ---------

                                   WORK LETTER
                                   -----------

         This Exhibit is attached to and made a part of this Amendment dated
July 10, 2000, by and between EOP-PERIMETER CENTER, L.L.C. ("Sublessor") and
INTERLIANT, INC. ("Sublessee") for space in the Building located at 64 Perimeter
Center East, Atlanta, Georgia 30346.


I.   Alterations and Allowance.
     -------------------------

     A.   Following the delivery of the Expansion Space by Sublessor, delivery
          of the Replacement Letter of Credit to Sublessor, and the full and
          final execution and delivery of this Amendment, Sublessee shall have
          the right to perform alterations and improvements in the Expansion
          Space (the "Initial Alterations"). Notwithstanding the foregoing,
          Sublessee and its contractors shall not have the right to perform
          Initial Alterations in the Expansion Space unless and until Sublessee
          has complied with all of the terms and conditions of Section 16 of the
          Sublease, including, without limitation, approval by Sublessor of the
          final plans for the Initial Alterations, including the demising wall
          referenced in Section B below, and the contractors to be retained by
          Sublessee to perform such Initial Alterations. Sublessee shall be
          responsible for all elements of the design of Sublessee's plans
          (including, without limitation, compliance with law, functionality of
          design, the structural integrity of the design, the configuration of
          the premises and the placement of Sublessee's furniture, appliances
          and equipment), and Sublessor's approval of Sublessee's plans shall in
          no event relieve Sublessee of the responsibility for such design.
          Sublessor's approval of the contractors to perform the Initial
          Alterations shall not be unreasonably withheld. The parties agree that
          Sublessor's approval of the general contractor to perform the Initial
          Alterations shall not be considered to be unreasonably withheld if any
          such general contractor (i) does not have trade references reasonably
          acceptable to Sublessor, (ii) does not maintain insurance as required
          pursuant to the terms of the Sublease, (iii) does not have the ability
          to be bonded for the work in an amount of no less 150% of the cost of
          the Initial Alterations, (iv) does not provide current financial
          statements reasonably acceptable to Sublessor, or (v) is not licensed
          as a contractor in the state/municipality in which the Expansion Space
          is located. Sublessee acknowledges the foregoing is not intended to be
          an exclusive list of the reasons why Sublessor may reasonably withhold
          its consent to a general contractor.

     B.   In addition to Sublessee's Initial Alterations, Sublessee shall also
          install a demising wall, in compliance with applicable building codes,
          separating the Expansion Space from the balance of the space on the
          floor. Such demising wall shall be installed to Sublessor's reasonable
          satisfaction no later than one (1) week following the Expansion
          Effective Date. Sublessor shall reimburse Sublessee for the actual
          reasonable costs incurred by Sublessee in connection with the
          installation of the demising wall, not to exceed $10,000.00. If
          Sublessee fails to timely install the demising wall as required in
          Section B above, Sublessor may install the demising wall and Sublessee
          shall reimburse Sublessor for any actual reasonable costs incurred by
          Sublessor in connection with such work exceeding $10,000.00, plus
          Sublessee shall pay Sublessor an administrative fee of $1,000.00 to
          cover Sublessor's time incurred with the foregoing. Any sums required
          to be paid by Sublessee hereunder shall be deemed Rent under the
          Sublease.

     C.   Sublessee agrees to accept the Expansion Space in its "as-is"
          condition and configuration, it being agreed that Sublessor shall not
          be required to perform any work or, except as provided in Section B
          above with respect to the demising wall, incur any costs in connection
          with the construction or demolition of any improvements in the
          Expansion Space.

     D.   This Exhibit shall not be deemed applicable to any additional space
          added to the original Sublease Premises at any time or from time to
          time, whether by any options under the Sublease or otherwise, or to
          any portion of the original Sublease

                                       7
<PAGE>

          Premises or any additions to the Expansion Space in the event of a
          renewal or extension of the original Term of the Sublease, whether by
          any options under the Sublease or otherwise, unless expressly so
          provided in the Sublease or any amendment or supplement to the
          Sublease.

         IN WITNESS WHEREOF, Sublessor and Sublessee have entered into this
Exhibit as of the date first written above.


                                      SUBLESSOR:

                                      EOP-PERIMETER CENTER, L.L.C., a Delaware
                                      limited liability company

                                      By:  EOP Operating Limited Partnership, a
                                           Delaware limited partnership, its
                                           sole member

                                      By:  Equity Office Properties Trust, a
                                           Maryland real estate investment
                                           trust, its managing general partner


                                           By:  /s/ Jeff Sweeney
                                              ----------------------------------
                                           Name:    Jeff Sweeney
                                                --------------------------------
                                           Title:   V.P. Leasing
                                                 -------------------------------


                                      SUBLESSEE:

                                      INTERLIANT, INC., a Delaware corporation

                                      By:  /s/ Kristian Nelson
                                         ---------------------------------------
                                      Name:  Kristian Nelson
                                           -------------------------------------
                                      Title: SVP of Operations
                                            ------------------------------------

                                       8
<PAGE>

                                   EXHIBT C

                           FORM OF LETTER OF CREDIT

                         -----------------------------
                        [Name of Financial Institution]

                                              Irrevocable Standby
                                              Letter of Credit
                                              No. ______________________
                                              Issuance Date:______________
                                              Expiration Date: March 31, 2001
                                              Applicant: Interliant, Inc.

Beneficiary
-----------

EOP-Perimeter Center, L.L.C.
c/o Equity Office Properties Trust
2 North Riverside Plaza
Suite 2200
Chicago, Illinois 60606
Attention:  Regional Counsel - Southeast Region

Ladies/Gentlemen:

         We hereby establish our Irrevocable Standby Letter of Credit in your
favor for the account of the above referenced Applicant in the amount of One
Hundred Ninety One Thousand Five Hundred Eighty One and 75/100 U.S. Dollars
($191,581.75) available for payment at sight by your draft drawn on us when
accompanied by the following documents:

1.       An original copy  of this Irrevocable Standby Letter of Credit.

2.       Beneficiary's dated statement purportedly signed by one of its officers
         reading: "This draw in the amount of ______________________ U.S.
         Dollars ($____________) under your Irrevocable Standby Letter of Credit
         No. ____________________ represents funds due and owing to us as a
         result of the Applicant's failure to comply with one or more of the
         terms of that certain sublease agreement dated May 29, 1998, as amended
         from time to time, by and between EOP-PERIMETER CENTER, L.L.C., a
         Delaware limited liability company, as landlord, and INTERLIANT, INC.,
         a Delaware corporation, as tenant."

         It is a condition of this Irrevocable Standby Letter of Credit that it
will be considered automatically renewed for a one year period upon the
expiration date set forth above and upon each anniversary of such date, unless
at least 60 days prior to such expiration date or applicable anniversary
thereof, we notify you in writing by certified mail, return receipt requested,
that we elect not to so renew this Irrevocable Standby Letter of Credit. A copy
of any such notice shall also be sent to: Equity Office Properties Trust, 2
North Riverside Plaza, Suite 2200, Chicago, IL 60606, Attention: Treasury
Department.

In addition, provided that you have not provided us with written notice, prior
to the effective date of any reduction described below, of Applicant's failure
to pay all sums when due under the referenced lease during the 12 months
preceding the effective date of any such reduction, the amount of this
Irrevocable Standby Letter of Credit shall automatically reduce in accordance
with the following schedule:

Effective Date of Reduction             New Reduced Amount of Letter of Credit

July 1, 2001                            $183,581.75
July 1, 2002                            $175,581.75
July 1, 2003                            $167,581.75

In addition to the foregoing, we understand and agree that you shall be entitled
to draw upon this Irrevocable Standby Letter of Credit in accordance with 1 and
2 above in the event that we elect not to renew this Irrevocable Standby Letter
of Credit and, in addition, you provide us with a

                                       9
<PAGE>

dated statement purportedly signed by one of Beneficiary's officers stating that
the Applicant has failed to provide you with an acceptable substitute
irrevocable standby letter of credit in accordance with the terms of the above
referenced lease. We further acknowledge and agree that: (a) upon receipt of the
documentation required herein, we will honor your draws against this Irrevocable
Standby Letter of Credit without inquiry into the accuracy of Beneficiary's
signed statement and regardless of whether Applicant disputes the content of
such statement; (b) this Irrevocable Standby Letter of Credit shall permit
partial draws and, in the event you elect to draw upon less than the full stated
amount hereof, the stated amount of this Irrevocable Standby Letter of Credit
shall be automatically reduced by the amount of such partial draw; and (c) you
shall be entitled to assign your interest in this Irrevocable Standby Letter of
Credit from time to time without our approval and without charge. In the event
of an assignment, we reserve the right to require reasonable evidence of such
assignment as a condition to any draw hereunder.

     This Irrevocable Standby Letter of Credit is subject to the Uniform Customs
and Practice for Documentary Credits (1993 revision) ICC Publication No. 500.

     We hereby engage with you to honor drafts and documents drawn under and in
compliance with the terms of this Irrevocable Standby Letter of Credit.

     All communications to us with respect to this Irrevocable Standby Letter of
Credit must be addressed to our office located at __________________________ to
the attention of _______________________.

                                        Very truly yours,

                                        _______________________

                                                 [name]
                                        _______________________

                                                 [title}
                                        _______________________

                                       10